1. Field of the Invention
The present invention relates to a device combination system which includes a plurality of devices each having a circuit operated by being supplied with power and which has such a structure that a battery is mounted on at least one power supply device. A plurality of devices including the power supply device which are optionally selected from the above plurality of devices, are combined with each other and operated by being supplied with power from the power supply device.
2. Description of the Related Art
Many apparatuses operated by a battery have a battery check function. In recent years, since many types of batteries are available, some apparatus are also provided with a battery type detecting function (refer to, for example, Japanese Patent Application Laid-Open Nos. 5-37828 and 11-194157).
The technique proposed by the apparatus disclosed in Japanese Patent Application Laid-Open No. 5-37828 is such that the type of a battery is notified to a controller in the apparatus through a mode button, an operation stop voltage is set by the controller as a threshold value according to the type of the battery, and when the threshold value is exceeded, the controller issues a warning. The technique proposed by Japanese Patent Application Laid-Open No. 11-194157 is similar to the above technique except that the type of a battery is automatically detected by the voltage output from the battery in place of the mode button.
Further, some of the apparatuses having the battery check function as described above extend the operating time of apparatuses by reducing power supplied from a battery to a load when the remaining amount of power in the battery decreases (refer to Japanese Patent Application Laid-Open No. 7-31067).
In recent years, various device combination systems are arranged by detachably mounting various devices such as a display device, a printer, and the like on devices such as a digital camera and a mobile phone, and the like. Among these device combination systems, there are systems arranged such that a digital camera, a mobile phone, and the like, for example, act as a power supply device and supplies power to a device, for example, an external display device mounted on the digital camera and the mobile phone.
In general, apparatuses such as the digital camera, the mobile phone, and the like, which are operated by a battery, have the battery check function as described above, and when the digital camera or the mobile phone is operated independently, the battery check function thereof operates accurately and precisely notifies a user of timing at which the battery is to be replaced.
However, when the device combination systems as described above are arranged, there is a possibility that the battery check function built in the digital camera and the mobile phone that acts as the power supply device does not work well.